YouTube has sent a legal letter to a popular video download stream ripping website, threatening to take legal action if the site doesn't remove the ability for users to download and convert copies of video streams uploaded to the YouTube platform. The owner of TubeNinja, the site in question, has pledged to ignore the warning and continue operating as usual.

We recently reported that the use of stream ripping sites is gaining steam among music fans who wish to pirate copies of songs by using the sites to download tracks. The use of the sites on which users can copy the URLs of videos from YouTube or songs from SoundCloud and convert them to downloadable mp3s grew by 25 percent last year.

One reason for that growth is the ease of use and the fact that users face no consequences from it, and it hasn't officially been deemed illegal. YouTube attempted several years ago to take down one of the biggest stream ripping sites, Youtube-mp3.org, by threatening legal action, but that site is still in business and remains one of the most popular video download services.

The new letter from YouTube gives TubeNinja 7 days to "stop offering (the) functionality ... designed to allow users to download content from YouTube." It accuses TubeNinja of violating the YouTube terms of service and API and warns that "continuing to violate these restrictions may result in legal consequences."

The owner of TubeNinja, however, who uses only his first name, Nathan, is pledging to continue operating and that users of the service are "responsible for the legitimacy of the content" they use it for. He also questions why Google, which owns YouTube, allows for the use of Chrome browser extensions that do exactly what his service offers and questions the legitimacy of any legal case that purports to require that stream ripping services be disabled. "The fact that services like Savefrom, Keepvid, clipconverter etc have been around since 2008, we find it hard to believe that there is any legal case at all," states Nathan. "Kind of like suing a maker of VHS-recorders for users taping the television broadcast."